[patch 123/147] vsprintf: rework bitmap_list_string

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From: Yury Norov <yury.norov@xxxxxxxxx>
Subject: vsprintf: rework bitmap_list_string

bitmap_list_string() is very ineffective when printing bitmaps with long
ranges of set bits because it calls find_next_bit for each bit in the
bitmap.  We can do better by detecting ranges of set bits.

In my environment, before/after is 943008/31008 ns.

[yury.norov@xxxxxxxxx: don't increment buf in bitmap_list_string]
  Link: https://lkml.kernel.org/r/20210817193735.269942-1-yury.norov@xxxxxxxxx
Link: https://lkml.kernel.org/r/20210814211713.180533-18-yury.norov@xxxxxxxxx
Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
Tested-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
Cc: Alexander Lobakin <alobakin@xxxxx>
Cc: Alexey Klimov <aklimov@xxxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 lib/vsprintf.c |   24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

--- a/lib/vsprintf.c~vsprintf-rework-bitmap_list_string
+++ a/lib/vsprintf.c
@@ -1241,20 +1241,13 @@ char *bitmap_list_string(char *buf, char
 			 struct printf_spec spec, const char *fmt)
 {
 	int nr_bits = max_t(int, spec.field_width, 0);
-	/* current bit is 'cur', most recently seen range is [rbot, rtop] */
-	int cur, rbot, rtop;
 	bool first = true;
+	int rbot, rtop;
 
 	if (check_pointer(&buf, end, bitmap, spec))
 		return buf;
 
-	rbot = cur = find_first_bit(bitmap, nr_bits);
-	while (cur < nr_bits) {
-		rtop = cur;
-		cur = find_next_bit(bitmap, nr_bits, cur + 1);
-		if (cur < nr_bits && cur <= rtop + 1)
-			continue;
-
+	for_each_set_bitrange(rbot, rtop, bitmap, nr_bits) {
 		if (!first) {
 			if (buf < end)
 				*buf = ',';
@@ -1263,15 +1256,12 @@ char *bitmap_list_string(char *buf, char
 		first = false;
 
 		buf = number(buf, end, rbot, default_dec_spec);
-		if (rbot < rtop) {
-			if (buf < end)
-				*buf = '-';
-			buf++;
-
-			buf = number(buf, end, rtop, default_dec_spec);
-		}
+		if (rtop == rbot + 1)
+			continue;
 
-		rbot = cur;
+		if (buf < end)
+			*buf = '-';
+		buf = number(buf + 1, end, rtop - 1, default_dec_spec);
 	}
 	return buf;
 }
_




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